1. Field of the Invention
The present invention relates to a film-forming composition. More specifically, the present invention relates to an insulating film having good film properties such as dielectric constant and mechanical strength for use in an electronic device and the like.
2. Description of the Related Art
In the field of electronic materials, with recent progress of high integration, multifunction and high performance, the circuit resistance and the capacity of a capacitor between wirings are increased and this leads to increase in the electric power consumption and delay time. Particularly, increase in the delay time becomes a large factor for the reduction in the signal speed of a device and the generation of crosstalk and therefore, reduction in the parasitic resistance or parasitic capacity is required so as to provide a high-speed device by reducing this delay time. For reducing the parasitic capacity, one specific countermeasure attempted is to cover the periphery of wiring with a low dielectric interlayer insulating film. The interlayer insulating film is required to have excellent heat resistance enough to withstand the thin film formation step at the production of a mounting substrate or the post step such as chip connection and pin attachment and also have chemical resistance enough to withstand a wet process. Furthermore, the wiring is recently shifting from Al wiring to low-resistance Cu wiring and along with this trend, flattening by CMP (chemical mechanical polishing) becomes a common practice. Thus, mechanical strength sufficiently high to withstand this process is demanded.
As for the insulating film with high heat resistance, polybenzoxazole and polyimide are widely known. However, since these contain an N atom having high polarity, an insulating film satisfied in view of low dielectricity, low water absorption, durability and hydrolysis resistance is not yet obtained.
Furthermore, most of organic polymers in general exhibit insufficient solubility in an organic solvent and how to prevent the precipitation in the coating solution or the generation of particles in the insulating film is an important problem to be solved. When the polymer main chain is modified to have a folded structure so as to increase the solubility, this disadvantageously causes reduction in the glass transition point and the heat resistance and it is not easy to satisfy both of these properties at the same time.
Also, a highly heat-resistant resin having a polyarylene ether as the basic main chain is known and the relative dielectric constant thereof is from 2.6 to 2.7. However, in order to realize a high-speed device, more reduction in the dielectric constant is demanded, and the relative dielectric constant as a bulk without porosification is preferably reduced to 2.6 or less, more preferably 2.5 or less.
An insulating film using a thermal polymer of an ethynyl group-substituted adamantane is disclosed in JP-A-2003-292878 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”). However, since this monomer is polymerized without using a polymerization catalyst, the reaction takes a long time and this causes a problem, for example, an undesired side reaction such as air oxidation proceeds, as a result, the relative dielectric constant of the obtained insulating film becomes high or a polymer sparingly soluble in a coating solvent is produced in a large amount as a by-product to worsen the surface state.
Furthermore, a polymer capable of thin film formation using an biadamantane monomer having a carbon-carbon triple bond as a polymerizable group is not known, and a case succeeded in forming a low dielectric thin film from this polymer is also not known.